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Find the third quartile class and frequency of the class from the given graph. How many students are there above the class? enter image description here My attempt : Here, $N=120$. Third quartile lies in $\frac {3N}{4}$item. $$=90 item$$ So, $Q_3 class = 20-30$.

but I couldn't do that second part of the question. Please help. Thanks

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    I would say that the corresponding x-value to the y-value of $90$ is $25$. And the corresponding x-value to the y-value of $60$ is 10. Therefore $Q_3$ class goes from $10$ to $25$. – 2017-01-21
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    @callculus, why do you take $60$ on the y axis. – 2017-01-21
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    @NeWtoN I feel $20$ should be the answer but I have no idea why the book says $30$. If I get the answer with steps, I will post it. – 2017-01-28
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    Ok. But, @ Rohan for the last question, I have an idea that Upper quartile is $25%$ in the more than ogive curve which yields 30. Am I correct Here? – 2017-01-28

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Here, You have got the $Q_3$ class as $(20-30)$.

Upper limit of the class touches the less than curve at $100$

Lower limit of the class touches the less than curve at $80$. So, frequency of the class $=100-80=20$.

Also, Corresponding frequency of upper limit of the third quartile class in the more than curve is $20$. So, the number of students above the class is $20$.

.....))